CRYPTOGRAPHY & NETWOK SECURITY- Symmetric key Ciphers

CRYPTOGRAPHY & NETWOK
SECURITY- Symmetric key
Ciphers
Dr R Jegadeesan Prof-CSE
Jyothishmathi Institute of Technology and Science,
karimnagar

Symmetric & Asymmetric key Ciphers
Syllabus
UNIT – II: Symmetric key Ciphers: Block Cipher principles, DES, AES, Blowfish, RC5,
IDEA, Block cipher operation, Stream ciphers, RC4. Asymmetric key Ciphers: Principles of
public key cryptosystems, RSA algorithm, Elgamal Cryptography, Diffie-Hellman Key
Exchange, Knapsack Algorithm.
Objective of DES
2

Aim & Objective :
❏ To review a short history of DES
❏ To define the basic structure of DES
❏ To describe the details of building elements of DES
❏ To describe the round keys generation process
❏ To analyze DES
UNIT – II: Symmetric key Ciphers: Block Cipher principles, DES, AES, Blowfish, RC5,
IDEA, Block cipher operation, Stream ciphers, RC4. Asymmetric key Ciphers: Principles of
public key cryptosystems, RSA algorithm, Elgamal Cryptography, Diffie-Hellman Key
Exchange, Knapsack Algorithm.
Objective of DES
3

The Data Encryption Standard (DES) is a symmetric-key block
cipher published by the National Institute of Standards and
Technology (NIST).
In 1973, NIST published a request for proposals for a national
symmetric-key cryptosystem. A proposal from IBM, a modification of
a project called Lucifer, was accepted as DES. DES was published in
the Federal Register in March 1975 as a draft of the Federal
Information Processing Standard (FIPS).
Introduction & History
4

DES is a block cipher, as shown in Figure 6.1.
Figure 6.1 Encryption and decryption with DES
Overview
5

Figure 6.2 General structure of DES
General structure of DES
6

Figure 6.3 Initial and final permutation steps in DES
Initial and Final Permutations
7

DES uses 16 rounds. Each round of DES is a Feistel cipher.
Round Function
8
Figure 6.4
A round in DES
(encryption site)

The heart of DES is the DES function. The DES function applies a 48-bit key to the rightmost 32 bits to
produce a 32-bit output.
DES Function
9
Figure 6.5
DES function

Expansion P-box
Since RI−1 is a 32-bit input and KI is a 48-bit key, we first need to expand RI−1 to 48 bits.
Expansion P-box
10
Figure 6.6 Expansion permutation

Although the relationship between the input and output can be defined mathematically, DES uses Table
6.2 to define this P-box.
Expansion P-box Table
11
Table 6.6 Expansion P-box table

S-Boxes
The S-boxes do the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit
output. See Figure 6.7.
S-boxes
12
Figure 6.7 S-boxes

S-Box rule
The S-boxes do the real mixing (confusion). DES uses 8 S-boxes, each with a 6-bit input and a 4-bit
output. See Figure 6.7.
S-box rules
13
Figure 6.8 S-box rule

S-Box
Table 6.3 shows the permutation for S-box 1. For the rest of the boxes see the textbook.
S-box Table
14

UNIT-II : Symmetric & Asymmetric key Ciphers
Table 6.11 Straight permutation table
Straight Permutation
15

UNIT-II : Symmetric & Asymmetric key Ciphers
Figure 6.9 DES cipher and reverse cipher for the first approach
DES cipher and reverse cipher approach
16

Figure 6.10
Key generation
Key generations
17

Text & Reference Books
18
Book Details :
TEXT BOOKS:
1. Cryptography and Network Security – Principles and Practice: William Stallings, Pearson
Education, 6th Edition
2. Cryptography and Network Security: Atul Kahate, Mc Graw Hill, 3rd Edition
REFERENCE BOOKS:
1. Cryptography and Network Security: C K Shyamala, N Harini, Dr T R Padmanabhan, Wiley
India, 1st Edition.
2. Cryptography and Network Security : Forouzan Mukhopadhyay, Mc Graw Hill, 3rd Edition
3. Information Security, Principles, and Practice: Mark Stamp, Wiley India.
4. Principles of Computer Security: WM. Arthur Conklin, Greg White, TMH
5. Introduction to Network Security: Neal Krawetz, CENGAGE Learning
6. Network Security and Cryptography: Bernard Menezes, CENGAGE Learning

Video reference
19
Video Link details (NPTEL, YOUTUBE Lectures and etc.)
•https://nptel.ac.in/courses/106105031/
•https://nptel.ac.in/courses/106105162/
•http://www.nptelvideos.in/2012/11/cryptography-and-network-
security.html

Security courses
20
courses available on <www.coursera.org>, and http://neat.aicte-india.org
https://www.coursera.org/
Course 1 : Introduction to Cyber Security
Cyber Security. An introduction to modern information and system protection technology and
methods.
Course 2: Cyber security Specialization
-Cyber security Fundamentals. Construction of Secure Systems

Security Tutorials
21
Tutorial topic wise
➢Cryptography Tutorial – Tutorialspoint www.tutorialspoint.com › cryptography
➢Cryptography Introduction – GeeksforGeeks www.geeksforgeeks.org › cryptography-
introduction
➢www.cse.iitm.ac.in › ~chester › courses › slides › 01_ Introduction

Network Security MCQs
22
CNS – MCQs
1.Cryptography, a word with Greek origins, means
a. Corrupting Data b. Secret Writing
c. Open Writing d. Closed Writing
2.A transposition cipher reorders (permutes) symbols in a
a. block of packets b. block of slots
c. block of signals d. block of symbols
3.The cipher feedback (CFB) mode was created for those situations in which we need to send
or receive r bits of
a. Frames b. Pixels c. Data d. Encryption
4.In Cryptography, when text is treated at the bit level, each character is replaced by
a. 4 Bits b. 6 Bits c. 8 Bits d. 10 B its
a. 5.The Advanced Encryption Standard (AES) was designed
a. National Institute of Standards and Technology b. IBM
c. HP d. Intel

Security Tutorial
23
CNS –Tutorial Problems:
The input to S-box 1 is 100011. What is the output?
If we write the first and the sixth bits together, we get 11 in binary, which is 3 in decimal. The
remaining bits are 0001 in binary, which is 1 in decimal. We look for the value in row 3, column 1,
in Table 6.3 (S-box 1). The result is 12 in decimal, which in binary is 1100. So the input 100011
yields the output 1100.
The input to S-box 8 is 000000. What is the output?
If we write the first and the sixth bits together, we get 00 in binary, which is 0 in decimal. The
remaining bits are 0000 in binary, which is 0 in decimal. We look for the value in row 0, column 0,
in Table 6.10 (S-box 8). The result is 13 in decimal, which is 1101 in binary. So the input 000000
yields the output 1101.

CNS Questions
24
Universities & Important Questions:
1. State Euler’s Theorem,
2. Define Diffusion and Confusion.
3. Brief the strengths of Triple DES.
4. Describe meet-in-the-middle-attack
5. What are the essential steps to be taken to encrypt a data using public key cryptography.
6. What is factoring problem?
7. What is called avalanche effect?
8. Describe the use of S-Box in DES algorithm
9. What is an elliptic curve?
10. What is the role of the public key authority in key distribution system?
11. Explain possible attacks on RSA algorithm
12. State the requirements for message authentication?
13. What is message authentication?

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